Dot printing apparatus



Sept. 16, 1969 w. G. PAIGE 3,467,232

DOT PRINTING APPARATUS Filed Aug. 31. 1967 2 Sheets- Sheet 1 p 16, 69 w. G. PAIGE 3,467,232

DOT PRINTING APPARATUS Fi'led Aug. 31, 1967 2 Sheets-Sheet 2 "mwm United States Patent U.S. Cl. 1971 12 Claims ABSTRACT OF THE DISCLOSURE A dot printing head having a plurality of printing elements or styli each with an impact surface on one end. The ends of the styli with the impact surfaces are selec tively extendible. The styli are arranged to lie in an approximately conical, geometric surface such that the ends of the styli with the impact surfaces form a line when extended. This stylus arrangement is particularly well adapted to electromagnetic actuation of the styli. In such case, an annular permanent magnet with an axially polarized field is placed around the opposite ends of the styli from the impact surfaces and the styli are selectively actuated by electric coils attached to the individual styli. The printing apparatus is arranged so the paths of travel of a roll of paper on which the characters are printed and an inked ribbon lie in the same plane. As the paper and inked ribbon pass between the printing head and the platen, the paper is situated between the printing head and the inked ribbon. The inked ribon is wrapped around the platen, which serves to reverse the direction of ribbon travel.

BACKGROUND OF THE INVENTION This invention relates to dot printing apparatus and, more particularly, to an improved dot printing head and component arrangement.

In the so-called dot or matrix printer, visual characters are formed by groups of dots imprinted on paper. Each dot is produced by driving an impact surface on one end of an elongated printing element against a platen with the paper and an inked ribbon disposed between the printing element and the platen. Commonly, a plurality of printing elements are arranged in parallel to form a line transverse to the direction of travel of the paper. As the paper travels past the printing elements, the dots are produced in parallel, i.e., a row at a time, by selectively actuating the printing elements according to the characters to be printed. Typical of this class of printer is the apparatus disclosed in my patent entitled High Speed Dot Printer that issued Nov. 16, 1954, as Patent No. 2,694,362.

A dot printer is capable of producing a large number of different characters with relatively few printing elements. For example, the entire alphabet and all the Arabic numerals can be well formed by a line of seven printing elements operating in parallel. Further, data transmission does not have to be synchronized to the operation of a dot printer as with other types of printers. The use of a small number of printing elements operating asynchronously pemits a compact, mechanically simple arrangement in which each of the printing elements must only move a short distance from its rest position to make impact with the platen. Consequently, high-speed, reliable printer operation is possible.

The reliability of dot printers is further enhanced because a large degree of reundancy is inherent in their operation. If the apparatus malfunctions momentarily or an erroneous input command is given, the intended character is still frequently recognizable from the correctly imprinted dots of the character.

In a dot printer, provision must be made for selectively actuating the printing elements to imprint the dots on the paper. The actuating mechanisms are of necessity located in the vicinity of their respective printing elements. Thus, space occupied by the actuating mechanism places a limit on the distance between the parallel printing elements in a line and, accordingly, the size of the characters. In an attempt to increase the concentration of the dots so the size of the letters can be made smaller, slow-responding actuating mechanisms are sometimes resorted to because of their compact size. This offsets to some extent the speed advantage of a dot printer. Sometimes, less reliable actuating mechanisms or actuating mechanisms delivering more inconsistent impact forces are selected on the basis of size considerations. This adversely affects the appearance of the resulting characters.

It is desirable to arrange the components of a dot printer so the characters can be read immediately after they are formed by the printing elements. In particular, the paths of travel of the inked ribbon and the paper are designed so the inked ribbon does not block a view of the paper after printing has taken place. Thus, in my above-mentioned patent, the inked ribbon and the paper travel in paths that lie in perpendicular planes. This creates problems, however, in coordinating the advancement of the paper, especially if a single-use inked ribbon is employed.

SUMMARY OF THE INVENTION In one aspect of the invention a dot printing head is provided with a plurality of elongated printing elements each having an impact surface on one end. The ends of the printing elements with the impact surfaces are selectively extendible to imprint dots on paper. The printing elements are aranged to lie in an approximately conical, geometric surface such that the ends of the printing elements with the impact surfaces form a line when extended. Most advantageously, the geometric surface is a right circular cone around which the printing elements are distributed at approximately equispaced intervals. The described arrangement of printing elements permits a plurality of extremely closely spaced dots to be simultaneously imprinted because the ends of the printing elements with the impact surfaces converge. Conversely, the opposite ends of the printing elements diverge, so a good deal of space is available for actuating mechanisms. Preferably, the impact surfaces are parallel to one another so they all contact the platen squarely.

The conical arrangement of printing elements is particularly well suited for use with electromagnetic actuating mechanisms, which are in general fast operating and highly reliable. An annular, axially polarized magnet located in coaxial relationship with the cone provides a substantially uniform identical permanent magnetic field with respect to each printing element. An electric coil is mechanically coupled to each printing element. Upon energization of the coil, the corresponding printing element is extended. The substantially uniform identical permanent magnetic field provided to each coil by the annular magnet makes it possible to deliver an identical impact force to all the printing elements.

A feature of the invention involves the arrangement of the path of travel of the paper and the inked ribbon in the same plane. Specifically, the inked ribbon is wrapped around the platen to effect a reversal in the direction of tape travel, while the path of the paper extends between the printing head and the inked ribbon and continues laterally beyond the printing head after the characters are formed. Thus, the inked ribbon does not obstruct a visual inspection of the characters immediately after they are formed by the printing head.

3 BRIEF DESCRIPTION OF THE DRAWINGS The features of a specific embodiment of the invention are illustrated in the drawings in which:

FIG. 1 is a perspective view of dot printing apparatus particularly depicting the path of travel of the paper and inked ribbon;

FIG. 2 is a top view in section of the printing head shown in FIG. 1;

FIG. 3 is a side elevation view of the printing head of FIG. 2 with the cover and the end removed; and

FIG. 4 is a side elevation view of the end of a support mast in the printing head of FIG. 2.

DESCRIPTION OF A SPECIFIC EMBODIMENT In FIG. 1, the components of a dot printer are shown mounted on a deck plate 1. A roll 2 of single-use inked ribbon is rotatably mounted on deck plate 1. The inked ribbon extends tangentially from roll 2 and is wrapped around a guide roller 3 that introduces a 90-degree bend in the ribbon path. From guide roller 3, the inked ribbon extends to and is wrapped around a platen 4 that is rotatably mounted on deck plate 1. Platen 4 introduces a 180-degree bend in the ribbon path, thereby reversing the direction of ribbon travel. From platen 4, the inked ribbon extends between a pinch roller 5 and a capstan 6 to a guide roller 7 around which it is wrapped to form a 90-degree bend in the ribbon path. From guide roller 7, the inked ribbon extends to a take-up reel 8 rotatably mounted on deck plate 1. Normally, pinch roller 5 is held in spaced relationship from capstan 6 by a spring 9. Capstan 6 is continuously rotated by a motor (not shown). The inked ribbon is out of contact with capstan 6 until pinch roller 5 is actuated by means not shown, at which time the inked ribbon is pressed against capstan 6 and driven in substantially nonslipping engagement with it in the direction of the arrows. As the inked ribbon is pulled from roll 2 by pinch roller 5 and capstan 6, it is wound up on reel 8. Reel 8 is driven by a motor (not shown) through a slip clutch or belt so as to take up the inked ribbon as it is fed to take-up reel 8. Thus, the path of travel of the inked ribbon lies in a plane parallel to deck plate 1.

A roll 10 of paper is also rotatably mounted on deck plate 1. The paper extends tangentially from roll 10 and is wrapped around a guide roller 11. From guide roller 11, the paper extends in a substantially straight line to a point between a pinch roller 12 and a capstan 13. Between guide roller 11 and platen 4, the paper is contiguous to the inked ribbon. The impact surfaces of the printing elements of a dot printing head 14 are in proximity to platen 4. When the printing elements are extended, their impact surfaces form a line parallel to the axis of platen 4, driving the paper and inked ribbon against platen 4 to imprint dots on the paper. Pinch roller 12 is normally held in spaced relationship from capstan 13 by a spring 15. Capstan 13 is continuously driven by a motor (not shown). The rotation of capstan 13 could be synchronized to that of capstan 6 by a simple linkage under deck plate 1. A guide 16 and guide roller 11 maintain the paper out of contact with capstan 13 until it is pressed against capstan 13 by pinch roller 12, at which time capstan 13 drives the paper, pulling it past printing head 14 in the direction of the arrows. Pinch rollers 5 and 12 operate at the same time so inked ribbon is fed with paper. When the paper travels past guide 16, its path of travel is no longer guided and it passes into a storage container or onto the floor. Immediately after the characters are formed by printing head 14, they are visible to an observer because the direction of travel of the inked ribbon is reversed by platen 4.

FIG. 2 shows printing head 14 in cross section. An annular permanent magnet 20 is clamped between annular magnet holding members 21 and 22, which are made of iron or other ferromagnetic material. The relative positioning between members 21 and 22 is maintained by pins such as pin 23. Magnet 20 is axially polarized, i.e., the internal magnetic field of magnet 20 is parallel to its axis, designated 19 in FIG. 2. A mast 24 of nonmagnetic material extends in axial alignment with magnet 20 through openings in members 21 and 22 to a point substantially beyond the shell formed by magnet 20 and members 21 and 22. At one end, mast 24 has a flange 25 that fits into a recess in member 22. A screw 26 attaches flange 25 to members 21 and 22.

A plurality of cylindrical styli with approximately circular impact surfaces serve as the printing elements. They are arranged around mast 24 to lie in an approximately conical geometric surface. By the term geometric surface a surface in the geometric sense is meant as distinguished from a physical surface. In other words, it is an imaginary surface generated by movement of a line, which surface may or may not correspond to a physical surface of a tangible object. A cover 27 and an end cap 28 surround the styli. For the sake of clarity, FIG. 2 depicts only a single stylus, designated 29. A complete complement of styli, 29 through 35, is illustrated in FIG. 3, which is a front View of printing head 14 with cover 27, end cap 28, and the end of mast 24 removed. Although seven styli are employed in the specific embodiment, the number of styli in a printing head constructed according to the invention is only a matter of design choice. The major portion of the length of each stylus is relatively thick to enhance its structural rigidity, while the remainder of the length of each stylus is relatively thin in accordance with the size of the dots to be printed. The impact surface of stylus 29 that imprints dots is at end 18 (FIG. 2). The geometric surface in which the styli lie deviates from a. true cone sufficiently that, in the extended position, the impact surfaces of the styli are arranged in a line, preferably a substantially straight line. Most advantageously, the impact surfaces of the styli all lie in parallel planes so they contact platen 4 squarely when extended. In most cases, it is also preferable to distribute the styli to lie in an approximately right circular conical geometric surface with the styli approximately equally spaced from one another. This configuration allots substantially the same space to the actuating mechanism of each stylus.

The actuating mechanism for stylus 29 is shown in FIG. 2. The actuating mechanisms for the other styli, which are not shown, are identical to the actuating mechanisms for stylus 29. The end of stylus 29 opposite end 18 is atfixed to a coil bobbin 36. A coil 37 is also affixed to bobbin 36. A pole piece 38 has three sections with dilferent diameters. The section with the smallest diameter is press-fitted in a cylindrical recess 39 in member 22 to assure continuity of the magnetic circuit for magnet 20. At the junction of the lower two sections, a shoulder is formed that abuts member 22, thereby accurately locating the axial position of pole piece 38. Since the diameters of the sections decrease between members 21 and 22, stray flux is minimized. An annular air gap is formed between the section of pole piece 38 with the largest diameter and the surface of a hole 41 through member 21. Coil 37 and bobbin 36 move freely through this air gap together. A leaf spring 50 urges the end of bobbin 36 against pole piece 38 and provides guidance and support for stylus 29. An annular conductive common terminal 42 and small conductive tabular terminals 43 individual to styli 29 are molded into an annular insulative strip 44. Electrical leads 47 and 48, shown schematically, provide flexible connections to terminals 42 and 43. A pin 40 extends through a hole in bobbin 36 and prevents rotation of bobbin 36. Thus, the possibility of straining leads 47 and 48 is prevented. Common terminal 42 provides a permanent connection from the positive terminal of a battery (not shown) to coil 37 of each stylus. Terminal 43 provides a connection from the negative terminal of the battery to the coil of stylus 29 only when it is desired to actuate stylus 29. Tabular terminals similar to terminal 43 are provided for every other stylus. The styli are then selectively actuated by closing the circuit path from the negative terminal of the battery to the corresponding individual tabular terminal, thereby causing current to flow through the corresponding electric coil of the actuating mechanism. Terminals 42 and 43 and insulative strip 44, as well as a rigid stop 49 and spring 50, are attached to member 21 by a screw 51. When terminal 43 is not connected to the negative treminal of the battery, spring 50 biases the end of bobbin 36 against pole piece 38, so stylus 29 is retracted. A low-reluctance path for the external magnetic field of magnet between its north and south poles is provided through member 21, pole piece 38, and member 22. When coil 37 is energized, the magnetic field of magnet 20 moves coil 37 axially away from pole piece 38. Consequently, stylus 29 is extended. Stop 49 limits the deflection of spring 50 and, thus, the axial position of stylus 29 in the extended position. Coil 37 is guided by the adjacent surfaces of member 21 and pole piece 38, and bobbin 36 is guided by pin 40 so that stylus 29 is confined to move axially with very little lateral play. As illustrated in FIG. 3, the radial displacement of the bobbins, and therefore the electric coils, from axis 19 is substantially uniform. In addition, the angle of elevation of the axis of each coil, i.e., the angle formed by the axis of the coil and a line lying in a plane perpendicular to axis 19, is the same. Moreover, the azimuth angle between each pair of adjacent coils, i.e., the angle formed between the projections of the axes of the pair of coils on a plane perpendicular to axis 19, is the same. As a result, the field strength of magnet 20 with respect to each coil is also the same. Since the current passing through each selected coil from the battery is also the same, an identical impact force is delivered by each stylus against platen 4.

Styli 29 through 35 pass out of printing head 14 through openings located at the interface between end cap 28 and an end portion 52 of mast 24. The end of mast 24 is illustrated in FIG. 4. As shown, end portion 52 has seven flat, tapered surfaces, each slopnig at the same angle as the slope of the contiguous stylus. The center of end cap 28 is cut out so end portion 52 fits into end cap 28 and forms therewith a disc-shaped body. End cap 28, which is preferably made of Teflon or another lowfriction material, is attached to mast 24 at a point 54 by a screw 53. One half of the cross section of each stylus hole is formed in the surface of end portion 52, and the other half is formed in the surface of end cap 28. These stylus holes guide the styli as they are extended and re tracted. The styli are also represented schematically in FIG. 4 with phantom lines. All the styli are depicted in their extended position so their impact surfaces are ar ranged in a straight line 55.

All the parts of printing head 14 that are not specifically designated as being made of ferromagnetic material are made of nonferromagnetic material.

What is claimed is:

1. A dot printing head comprising: a plurality of elongated, axially extendible printing elements each having an impact surface on one end, all the elements being arranged to lie approximately in a circular conical geometric surfaces, the axes of the elements extending in the opposite direction from the impact surfaces to a circular configuration.

2. The apparatus of claim 1, in which the printing elements are extended by an annular magnet and actuating mechanisms that extend the elements responsive to the field of the magnet, the actuating mechanisms being attached to the individual elements at substantially the same radial distance from the magnet.

3. The apparatus of claim 1, in which the angle between each printing element and the adjacent element is substantially the same for all the elements.

4. The printing head of claim 1, in which the ends of the printing elements with the impact surfaces are arranged to lie in a straight line when the printing elements are extended.

5. The printing head of claim 1, in which the elongated members are extended by magnet means and an electric coil aifixed to the end of each printing element opposite the impact surface, the electric coils being selectively energizable and being distributed in the field of the magnet means at points where the field strength is the same.

6. The printing head of claim 1, in which the axes of the printing elements all form substantially the same angle with the axis of the conical surface.

7. The printing head of claim 6, in which the ends of the printing elements opposite the impact surfaces are equally spaced around the circle.

8. Dot printing apparatus comprising: a plurality of styli each having an impact surface on one end; means for selectively extending the ends of the styli with the impact surfaces, the means for selectively extending the ends of the styli with the impact surfaces including an axially polarized annular magnet, and an electric coil affixed to the end of each stylus opposite the impact surface, the electric coils being selectively energizable and being distributed in the field of the magnet substantially equal radial distances from the axis of the magnet; and means for supporting the styli to lie approximately in a conical geometric surface, the ends of the styli opposite the impact surfaces being arranged to lie in a circle.

9. The apparatus of claim 8, in which the axes of the coils all form substantially the same angle with the axis of the conical surface.

10. Printing apparatus comprising: a rotatable cylindrical platen; a printing head spaced from the platen, the printing head comprising a plurality of elongated axially extendible styli each having an impact surface that moves against the platen when extended, all the styli being arranged to lie approximately in a circular conical geometric surface with the axes of the elements extending in the opposite direction from the impact surfaces to a circular configuration; a length of inked ribbon, a length of flexible material capable of receiving inked impressions from the impact surface; means for transporting the lengths in paths that lie in the same plane, the plane being perpendicular to the axis of rotation of the platen; and means for guiding the lengths between the platen and the printing head such that one length is wrapped around the platen to reverse its direction of travel and the other length passes straight by the platen to maintain its direction of travel.

11. Dot printing apparatus comprising: a plurality of styli each having an impact surface at one end; means for selectively extending the ends of the styli with the impact surfaces, the means for selectively extending the ends of the styli with the impact surfaces including an axially polarized annular magnet, and an electric coil fixed to the end of each stylus opposite the impact surface, the electric coils being selectively energizable and being distributed such that the angle formed between the axis of the conical surface and the axis of each coil is substantially the same; and means for supporting the styli to lie approximately in a conical geometrical surface, the ends of the styli opposite the impact surfaces being arranged to lie in a circle. 12. Dot printing apparatus comprising: a plurality of styli each having an impact surface on one end; means for selectively extending the ends of the styli with the impact surfaces; and means for supporting the styli to lie approximately in a conical geometric surface with the ends of the styli opposite the impact surfaces being arranged to lie in a circle, the styli supporting means includthe cap.

References Cited UNITED STATES PATENTS Gommel 197-151 XR Nelson 197-153 Thompson 101-93 XR Paige 197-1 XR 8 Lake et al. 101-93 XR Gates 197-151 Preisinger 101-93 Foley et a1 197-1 XR Sanborn 197-1 XR Bradshaw 101-93 Reach et a1. 101-93 EDGAR S. BURR, Primary Examiner US. Cl. X.R. 

